There are many circumstances in which a television screen display is required to superimpose one video image on top of another video image. In the past, such superimposed images were generally created at the source of the video signal as part of the programming. Today, there are more and more applications where it is desirable to be able to create superimposed video images both from the program source, and interactively based on a user input. Almost all televisions manufactured today are capable of interfacing with different sources of programmed materials providing a video input signal for display on the television screen, for example, a VCR, a digital versatile or video disk ("DVD") player, cable, DSS, etc. Further, some of those sources provide digital audio and video input signals in accordance with the Moving Picture Expert Group MPEG-2 audio/video digital compression standard. Thus, contemporary televisions preferably have the capability of processing digital input signals and providing digital signals representing the desired images. Most often, those digital signals are converted to analog signals for use by known analog television display units.
Further, most televisions manufactured today and/or their plug compatible program sources have user interactive capabilities that utilize menus of possible actions superimposed on the screen simultaneously with the display of program material. Using such superimposed menu displays, a user may choose to have captions or subtitles displayed on the screen. In other applications, the displayed menus may be used to provide desired adjustments or settings, for example, audio and video levels, game time, degree of difficulty, etc., which are unique to the user. Those settings are often displayed in the form of linear scales that change in response to a user input pushing a button.
When program sources provide information in digital form, the information is provided in a data packet. Preferably, the audio and main video data are provided in respective data packets in an "MPEG-2" format. However, the information relating to subvideo or superimposed video may be provided in a data packet in any one of several formats. For example, the superimposed video may be provided in a Subpicture format that is defined in the known Digital Video Display ("DVD") standard. The Subpicture format includes a header block, a pixel data block, and a command data block. Generally, the header is used to identify the general nature of the data. For example, the header may be used to identify the format of the data, whether the pixel data is compressed, if a command structure is used, how the data is to be read, etc. In the Subpicture format, the pixel data represents color and contrast information and is compressed using known compression techniques, for example, run length compression. The command data in the Subpicture format identifies the location and size of the subpicture, the location and size of highlight areas within the subpicture, and the location and size of one or more smaller areas within the subpicture that may have unique color and contrast values, etc.
In other applications, the superimposed video data associated with the main video may be in other formats. For example, an on-screen display format for a DVB/STB system presents the subvideo data in a format that generally includes only a header block and an uncompressed pixel data block. In addition, although invisible to the viewer, subvideo data can also be utilized during the vertical blanking interval ("VBI") between display fields or frames of a complete video image. In further applications, the subvideo data may also be provided in proprietary formats, such as a DSS format used with digital satellite transmissions; or the subvideo data may be in the form of raw pixel data that can be directly converted to analog signals for use by the display unit.
In the past, it was commercially feasible to market televisions that were designed to be compatible with only a single format, for example, the on-screen display format for superimposed video information. However, with the recent development and standardization of the digital Subpicture format defined by the DVD standard, there is a need for televisions to provide the capability of recognizing and processing different formats for superimposed video data.